This invention relates generally to devices for filtering and separating fluids. More particularly, the present invention relates to fuel filters for removing foreign particles and separating water from the fuel of the fuel supply system of an internal combustion engine.
The absence of high standards of quality control in diesel fuel supplies dictates that an effective fuel filter be incorporated into the fuel supply system of a diesel engine. Diesel fuel supplies frequently contain significant quantities of abrasive particles and water which present the potential for permanent damage to the components of the fuel injection pump, the fuel delivery system and the engine.
A multitude of conventional fuel filters employ a base which mounts a disposable filter cartridge. The cartridge is secured to the base by a collar which engages against a roll seam structure of the cartridge. The disposable filter cartridge is replaced at pre-established intervals of filter usage. In some conventional embodiments, the cartridge includes a single stage filter system wherein fuel flows axially and radially through a filter element for removing particulate matter. Filtered fuel flows axially and exits through an outlet passage of the base. The filter element may also function as a water barrier. The separated water may be collected in a sump and periodically removed.
When the filter cartridge is changed, air may be trapped in such filters forming an air pocket at the top of the fuel filter. For pressurized fuel delivery systems, the air pockets tend to be absorbed over time, into the filtered fuel. The air pockets generally do not result in the formation of large air bubbles in the fuel supply partly due to the vapor pressure of the pressurized fuel. Consequently, for pressurized systems, air pockets in the fuel filter generally do not present a significant problem or obstacle to the circulation of fuel through the fuel filter and the delivery of fuel to the engine.
However, in vacuum applications, the formation of air pockets in the fuel circulating through the filter can present a more significant problem. The initial air pocket may "vapor lock" the fuel filter, preventing the flow of fuel. The air pockets are much more resistant to absorption over time in vacuum systems. Moreover, the vacuum may result in the formation of tiny air bubbles or "gassing" in the fuel, especially as the filter element approaches the end of its useful life and the pressure drop across the filter media increases. This increasing restriction to flow causes more air to be pulled from the fuel as the differential pressure between the clean side and the dirty side increases. In and of themselves, these individual tiny bubbles do not present a problem to normal vehicle operation as they are easily ingested by the fuel injection pump. When subjected to pump charging pressures, the tiny bubbles are ordinarily reabsorbed by the fuel.
The problems in vacuum systems initially arise on the clean side of the filter element where the small bubbles inevitably collect, agglomerate and form air pockets, e.g., large bubbles. The large bubble formation will continue over a period of time until the physical attitude of the filter element changes due to vehicle maneuvering, etc. When these relatively large air pockets or bubbles escape into the fuel flow, they are not easily ingested and may cause engine operating problems such as stalling, stumbling or irregular idle.